For many years it has been general practice to utilize bottles which are sealed by means of the so-called crown closure to package products which effect a positive pressure in the bottles. Exemplary of such products are carbonated beverages such as beer, soda water and various well known soft drinks. The crown closure is commonly made of tinplate and its fluted skirt is engaged under a peripheral rib which extends around the neck of the bottle in close proximity to its mouth.
The crown closure suffers from two defects, i.e., it requires special tools to remove it from the bottle and it cannot be used to reclose the bottle. This latter disadvantage is important from the consumer acceptance standpoint when the container is of a capacity exceeding the size of a single serving as, with the crown closure, the consumer has no way of easily resealing the container to preserve the remaining product. To overcome this disadvantage, there is presently in the market place a widely used package that enables resealing of the container by the utilization of a closure threadable onto a container having an externally threaded neck. Achievement of the seal is generally effected by the utilization of a liner which is carried adjacent the top of the closure and which is dimensioned to make sealing contact with the container lip upon screwing of the closure to the container. With this threaded system, the consumer reseals the package by merely screwing the closure back onto the container. It has been found that to achieve an initial high fidelity seal, it is desirable to utilize a free-floating disc liner which is carried by the closure. This liner, since it is free-floating, need not necessarily follow the rotation of the closure as it is screwed onto or off of the container. In fact, it has been found highly desirable to optimize the free-floating feature by providing that the liner be of a material such that the liner exhibits a higher coefficient of friction between itself and the container lip than it does between itself and the top of the closure. By having this dissimilarity in the coefficients of friction, the liner will remain stationary with respect to the container lip but will be able to slip with respect to the turning closure as it is threaded onto the container. With the liner slipping vis-a-vis the closure, it does not rotate therewith and the liner is not rubbed around the top of the container lip. Without this slipping, liner-lip rubbing occurs and is disadvantageous as each irregularity in the container lip will cause its particular liner deformation and such deformations will, when the closure reaches its final tightened position, almost always not coincide with the particular lip irregularity which caused the liner deformation. The result of this non-coincidence is deleterious to seal fidelity as the contacting liner-lip sealing surfaces are not in as intimate contact as would be possible if the liner deformation matched the lip irregularity which caused it. However, with the liner slip, the liner is simply pressed downwardly onto the container lip and each liner deformation caused by a particular lip irregularity will coincide with the irregularity. With matching of the liner deformations to the lip irregularities, a highly intimate contact is made and seal fidelity is preserved. While this liner system is beneficial, it does suffer from one drawback, i.e., the system tends to exhibit backoff of the closure from the container. This tendency to backoff is believed to be due to the closure not being able to anchor itself to the liner (due to the built-in slip effect) and therefore not able to resist the unthreading forces which are always present when utilizing thermoplastic closures. This backing off of the closure is most pronounced when the container and closure thread angles are steep, i.e., about seven threads per inch.
Thus, it is an object of this invention to provide a closure which is resistant to backoff but which is also able to utilize a liner sealing system in which the liner exhibits a higher coefficient of friction between itself and the container lip than between itself and the closure.